linux-kernel - Re: [PATCH 02/25] mm: Introduce mm_fault

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Date:   Mon, 15 Jun 2020 15:32:40 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Xu <peterx@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 02/25] mm: Introduce mm_fault_accounting()

On Mon, Jun 15, 2020 at 3:16 PM Peter Xu <peterx@...hat.com> wrote:
>
> Provide this helper for doing memory page fault accounting across archs.  It
> can be defined unconditionally because perf_sw_event() is always defined, and
> perf_sw_event() will be a no-op if !CONFIG_PERF_EVENTS.

Well, the downside is that now it forces a separate I$ miss and all
those extra arguments because it's a out-of-line function and the
compiler won't see that they all go away.

Yeah, maybe some day maybe we'll have LTO and these kinds of things
will not matter. And maybe they already don't. But it seems kind of
sad to basically force non-optimal code generation from this series.

Why would you export the symbol, btw? Page fault handling is never a module.

              Linus